Fares available from $1366.23 roundtrip with Saturday night stay (fare code XK3X76B2). $110 more for main cabin. It's not that complicated.
We don't know the OP's dates (just April), but I suspect that the $3600 price is FULL Y or something close. I wonder whether the OP is inadvertently searching for a flexible/refundable/changeable ticket and that's kicking it into a high fare class. I'm assuming that there aren't stopovers so it's not a multicity ticket.